As known, tubular fabric usually comes out in rope-like form after dyeing operations. Firstly, the fabric needs to be untwisted, and then has to be widened transversally so as to carry out successive lengthwise cutting, opening and spreading operations.
Cutting is attained along the line determined by a missing weft. The position of such a line is continuously sensed by suitable reading means that are associated with a device for centering the fabric. Depending on the direction and displacement of the missing weft line relative to the central position, as sensed by the reading means, the centering device rotates the tubular fabric in either direction so as to get the missing weft line to face the cutting device precisely.
Besides accuracy, a basic requirement of the centering device is that it must be able to work at high speed. Rotation and counter-rotation must occur very quickly, not to limit the speed of advancement of the fabric. The fabric must necessarily be stretched to be able to react promptly to the stresses it is subjected to by the centering device. Also, wrinkles and overlapping of the fabric can be prejudicial to the accuracy with which the missing weft line is positioned, thereby compromising correct lengthwise cutting of the fabric.
There are known centering devices provided with idly mounted rollers that do not hinder lengthwise advancement of the fabric. By rotating transversally relative to the direction of advancement of the fabric, the rollers cause the fabric to rotate for centering the missing weft line on the cutting tool. However, conventional centering devices do not work on a stretched fabric. As a result, they are not capable of attaining required corrections of position quickly enough and therefore represent a "slow" point of the textile plant.